WhatsWrongWithThis????

[BurrMan]

Machineit,
I think your missing something...

Let me try to explain it to you this way.

The "Roughing" toolpath is a material "removal" program. I think you are viewing it as a material "Cutting" program... Think of your part you see in the viewport, as something being "Avoided"

The "5th pass" (actually the first one) is a pass at the same level as the pass of the surface just before it.. (All your stepping numbers and geometry numbers and tooling are equal divisions) The toolpath has determined it doesnt need to do the one just before it because the next path (At the exact same level) is going to remove that material...Rememeber, removing material, not cutting your part)

You can force that cut if you want by setting a step of .2499

The cutting air stuff is the toolpath actually cutting leftover material.

The Z-level rough is calculated by squares and decides its path based on that... The "stock selection" is actually limiting the toolpath like a boundry, because it is calcualting "removing material". So even though you see round toolpaths, as if it's cutting your round objects, it's actually just avoiding them..

You can see whats being cut by removing the stock definition, then re-calculating the toolpath. Watch the toolapath backplot. At the second level down, you will see the square being left by the cut. If you watch closely, for the "air pass", you will see geometry being cut in the backplot (Very small) The tool had to return to be sure to remove that geometry.

By the way.. Have you actually "entity summaried" the object being cut???

Try punch those numbers into the top and bottom of job and then see what the toolpath does!

I could make another video..

[Machineit]

The "5th pass" (actually the first one) is a pass at the same level as the pass of the surface just before it.. (All your stepping numbers and geometry numbers and tooling are equal divisions) The toolpath has determined it doesnt need to do the one just before it because the next path (At the exact same level) is going to remove that material...Rememeber, removing material, not cutting your part)

I do not want to argue material "Removal or Cutting," look at the part shape. It is supposed to be 3/4 inch tall on the top, 1/2 on the middle step and 1 inch on the bottom step. You can see that if you look at the drawing. That is what it is "removed" to if you run without top and bottom selected.

If you add the top and bottom of the part, the resulting material "removal" leaves a part that is 1/2 inch on top, 1/2 inch second step and 1 1/4 inch third step. Just look at the part you have left after Backplotting! You can clearly see it if you compare the two views, BobCad and Predator.

Watch the video again and count the steps for the last level and you will see that it makes five 1/4 inch passes for a total of 1.25 inches.

I'm not arguing procedure or preferences of machining here, just pointing out a glitch in the program when entering top and bottom.

I remember another part that I made that got changed when I added the top and bottom of the part, but at that time I thought I did something wrong and just eliminated the top and bottom and did not think about it again, until now. There is a bug or something that is in that part of the program.

I am not trying to bash BobCad, I'm just pointing out a bug. I respect you and all that you do here and I have defended you in other posts, but this is obviously a problem. Perhaps BobCad can fix this and help everyone out.

I used part of the program and added to it and took away and finished my parts on Friday, so this is now just academic.

Mike

[BurrMan]

Mike,
I dont feel like were arguing... I know what you are pointing out..

But did you entity summary your objects and look at the top and bottom Z values like I suggested?

I was just trying to point out the strategy that is being employed coupled with the "Constraints" being put on the geometry with the parameters, would, does and should change the toolpath...

[BurrMan]

Here's a video that talks about the Z-level rough operation, and how constraints placed on the op can change the toolpath calculated and the result.



Let me know if this helps at all.

[dnelso]

thanks burrman very good job with the illustration

[Machineit]

Excellent presentation, I understand what is going on now. Now, tell me why the top and bottom was .0002 off of what was drawn. I extracted the edges and they were correct at 0.0 and -2.25 and entities showed the same. As a solid though it was off the .0002. That is what threw to whole thing off.

Thanks again for your help.

[BurrMan]

Hi Mike,
"Bounds Data" is part of 3d geometry.. It's just a function of how NURBS work.

Here are 2 videos which can help to understand it, though not made for this example, it is the same.

Bounds data:



NURBS Trim boundries:



Usaually Programs hide this information from the user, because it's more about the underlying geometry definition... But it still exists. You can see happen in BobCad, by creating your part using the 3d cylider command and setting your values.. The entity summary will summary as you WERE expecting, although you will see the roughing toolpass perform as it has been, because it is reading the actuall 3d geometry for it's calculations.. You can then run the "extrude curve command" on the 2d geometry and the solids will summary with the bounds included and showing...

You can MAKE the roughing toolpath perform a "finish cut", with the underlying knowledge of whats happening, but most would just say, "It's the wrong toolpath to acheive the results you are looking for"....